day18-python之迭代器和生成器

1.文件处理模式b模式

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 # f=open('test.py','rb',encoding='utf-8') #b的方式不能指定编码
 # f=open('test.py','rb') #b的方式不能指定编码
 # data=f.read()
 # #'字符串'---------encode---------》bytes
 # #bytes---------decode---------》'字符串'
 # print(data)
 # print(data.decode('utf-8'))
 # f.close()

 # f=open('test.py','wb') #b的方式不能指定编码
 # f.write(bytes('1111\n',encoding='utf-8'))
 # f.write('杨件'.encode('utf-8'))

 # f=open('test.py','ab') #b的方式不能指定编码
 # f.write('杨件'.encode('utf-8'))

 # open('a;ltxt','wt')

2.读取大文件最后一行

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 f=open('test.txt','rb')

 for i in f:
     offs=-3
     n=0
     while True:
         f.seek(offs,2)
         data=f.readlines()
         if len(data) > 1:
             print('最后一行',data[-1].decode("utf-8"))
             break
         offs*=2

3.文件操作的其他方法

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 # f=open('a.txt','r+',encoding='utf-8')
 # data=f.read()
 # print(data)
 # f.write('你好')

 # f=open('a.txt','r+',encoding='latin-1')
 # data=f.read()
 # print(data)
 # f.write('aaaaaaaaaaa')

 # f=open('a.txt','r',encoding='utf-8',newline='') #读取文件中真正的换行符号
 f=open('a.txt','r+',encoding='utf-8',newline='') #读取文件中真正的换行符号
 #
 # print(f.closed)
 # print(f.encoding)
 # f.flush()
 # print(f.readlines())

 # print(f.tell())
 # f.readline()
 # print(f.tell())
 #
 # f.seek(1)
 # print(f.tell())
 # print(f.readlines())
 # f.seek(3)
 # print(f.tell())
 # print(f.read())

 # data=f.read(1)
 # print(data)

 f.truncate(10)

 # f.flush() #讲文件内容从内存刷到硬盘
 #
 # f.closed #文件如果关闭则返回True
 #
 # f.encoding #查看使用open打开文件的编码
 # f.tell() #查看文件处理当前的光标位置
 #
 # f.seek(3) #从开头开始算，将光标移动到第三个字节
 # f.truncate(10) #从开头开始算，将文件只保留从0-10个字节的内容，文件必须以写方式打开，但是w和w+除外
 #
 # f=open('a.txt','r',newline='')
 #
 # data=f.readline().encode('utf-8')
 # print(data)
 # print(f.tell())

 # f=open('seek.txt','r',encoding='utf-8')
 # print(f.tell())
 # f.seek(10)
 # print(f.tell())
 # f.seek(3)
 # print(f.tell())

 # f=open('seek.txt','rb')
 # print(f.tell())
 # f.seek(10,1)
 # print(f.tell())
 # f.seek(3,1)
 # print(f.tell())

 # f=open('seek.txt','rb')
 # print(f.tell())
 # f.seek(-5,2)
 # print(f.read())
 # print(f.tell())
 # f.seek(3,1)
 # print(f.tell())

 #
 # f=open('日志文件.txt','rb')
 # data=f.readlines()
 # print(data[-1].decode('utf-8'))

 f=open('日志文件.txt','rb')
 #
 # for i in f.readlines():
 #     print(i.decode('utf-8'))

 #循环文件的推荐方式
 # for i in f:
 #     print(i)

 for i in f:
     offs=-10
     while True:
         f.seek(offs,2)
         data=f.readlines()
         if len(data) > 1:
             print('文件的最后一行是%s' %(data[-1].decode('utf-8')))
             break
         offs*=2

4.迭代器和生成器

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-

 # x='hello'
 # # print(dir(x))
 # iter_test=x.__iter__()
 # #
 # print(iter_test)
 # print(iter_test.__next__())
 # print(iter_test.__next__())
 # print(iter_test.__next__())
 # print(iter_test.__next__())
 # print(iter_test.__next__())
 # print(iter_test.__next__())

 # l=[1,2,3]
 # for i in l:  #i_l=l.__iter_()  i_l.__next__()
 #     print(i)

 # index=0
 # while index < len(l):
 #     print(l[index])
 #     index+=1

 # iter_l=l.__iter__() #遵循迭代器协议，生成可迭代对象
 # print(iter_l.__next__())
 # print(iter_l.__next__())
 #
 # for i in l:
 #     print(i)

 # s={1,2,3}
 #
 # # for i in s:
 # #     print(i)
 # iter_s=s.__iter__()
 # print(iter_s)
 # print(iter_s.__next__())
 # print(iter_s.__next__())
 # print(iter_s.__next__())
 # print(iter_s.__next__())

 # dic={'a':1,'b':2}
 # iter_d=dic.__iter__()
 # print(iter_d.__next__())

 # f=open('test.txt','r+')
 # # for i in f:
 # iter_f=f.__iter__()
 # print(iter_f)
 # print(iter_f.__next__(),end='')
 # print(iter_f.__next__(),end='')
 # l=[1,2,3,4,5]
 # diedai_l=l.__iter__()
 # while True:
 #     try:
 #         print(diedai_l.__next__())
 #     except StopIteration:
 #         # print('迭代完毕了,循环终止了')
 #         break

 # l=['die','erzi','sunzi','chongsunzi']
 # #
 # iter_l=l.__iter__()
 # print(iter_l)
 # print(iter_l.__next__())
 # print(iter_l.__next__())
 # print(iter_l.__next__())
 # print(iter_l.__next__())
 # print(iter_l.__next__())
 # print(next(iter_l)) #next()---->iter_l.__next__()

 # def test():
 #     yield 1
 #     yield 2
 #     yield 3
 # g=test()
 # print('来自函数',g)
 # print(g.__next__())
 # print(g.__next__())
 # print(g.__next__())

 #三元表达式
 # name='alex'
 # # name='linhaifeng'
 # res='SB' if name == 'alex' else '帅哥'
 # print(res)

 #列表解析
 # egg_list=[]
 # for i in range(10):
 #     egg_list.append('鸡蛋%s' %i)
 # print(egg_list)

 # l=['鸡蛋%s' %i for i in range(10)]
 # # l1=['鸡蛋%s' %i for i in range(10) if i > 5 ]
 # # l1=['鸡蛋%s' %i for i in range(10) if i > 5 else i] #没有四元表达式
 # l2=['鸡蛋%s' %i for i in range(10) if i < 5] #没有四元表达式
 #
 # # print(l)
 # # print(l1)
 # print(l2)

 # laomuji=('鸡蛋%s' %i for i in range(10)) #生成器表达式
 # print(laomuji)
 # print(laomuji.__next__())
 # print(laomuji.__next__())
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 # print(next(laomuji))
 #
 l=[1,2,3,34]
 # map(func,l)
 #
 # print(sum(l))
 # print(sum())
 print(sum(i for i in range(10000000)))